The invention relates to a method of manufacturing a low-pressure mercury discharge lamp wherein a capsule containing mercury is arranged in a radiation-transmitting discharge vessel, after which the discharge vessel is provided with a rare gas and is closed, and wherein means for maintaining an electric discharge are arranged in or adjacent the discharge vessel and the capsule is opened after the discharge vessel has been closed, the capsule being opened by irradiation through a wall portion of the discharge vessel.
The invention also relates to a low-pressure mercury discharge lamp provided with a radiation-transmitting discharge vessel which is closed in a gastight manner and which contains an ionizable filling comprising mercury, while a capsule with a glass wall having an opening is arranged in the discharge vessel and the lamp is in addition provided with means for maintaining an electric discharge in a discharge space surrounded by the discharge vessel.
U.S. Pat. No. 4,278,908 describes a method of dosing mercury in a conventional low-pressure mercury discharge lamp, i.e. a low-pressure mercury discharge lamp provided with a tubular discharge vessel with an electrode positioned at either end, current supply conductors extending from each electrode to outside the discharge vessel. According to the U.S. Patent, the mercury is dosed by means of a glass capsule provided with a perforated metal envelope by means of which it is fastened to an end portion of the discharge vessel. In the known method, the capsule is heated in that the lamp is positioned in a high-frequency magnetic field. Eddy currents arise in the metal envelope of the capsule then, which lead to a heat generation which cause the glass capsule to melt at the area of the perforation, so that the mercury present in the capsule becomes available in the discharge vessel.
It is a disadvantage that the metal envelope of the capsule forms an additional component which involves additional manufacturing, storage, transport, and assembling costs.
From DE-OS 2 340 885 (U.S. Pat. No. 3,913,999) a method of manufacturing a fluorescent lamp is known according to which an aluminum, mercury containing capsule is opened by irradiation through a wall portion of the discharge vessel.
According to this method a radiation source aims a narrowing beam of radiation at the capsule such that the beam is wide in the location where it passes through the wall portion of the discharge vessel compared with a focal spot of the beam which coincides with the wall of the capsule. It is a disadvantage of this method that the radiation intensity at the area of the capsule wall is dependent on the distance to the radiation source. Furthermore, it is a disadvantage that the discharge vessel may become damaged if the focal spot of the beam approaches the wall of the discharge vessel to closely. Therefore, the lamp must be accurately positioned during irradiation.